This invention relates to electric cable joints (including joints between dis-similar conductors, often called `terminations`, as well as joints between similar conductors, always called `joints`) primarily (but not exclusively) for screened cables working at voltages in the approximate range from 1 to 35 kV.
Three types of joint are in regular use in this range:
1. Cast resin joints (such as the applicants' `Bicast` and `Bithane` joints). These are effective and reliable in service, but they do not avoid the need for taping operations, and the shelf life of the resins is limited.
2. Slip-on joints (such as the applicants ' Bimold joints) made from pre-moulded resilient components interference-fitted together and to the cable or cables. These are also effective and reliable when satisfactorily made, and the parts are of precise dimensions and can be factory-tested; and if necessary the joint can be taken to pieces and the parts re-used. However, joints of this type have a very limited tolerance range which makes them difficult to assemble if the cable is a little oversize and risks electrical breakdown if a slip-on component is used on a cable only a little below the correct size.
3. Heat-shrink joints (such as the applicants' `Bitherm` joints at the lower end of the voltage range). These are versatile and convenient but because the heat treatment to produce shrinkage cannot be precisely controlled, have unpredictable finished dimensions in the longitudinal direction (and sometimes unpredictable shapes), which may complicate the design of associated cable supports or other equipment; discharge testing is impracticable, and the parts can only be separated destructively.